Various types of lighting devices are produced to meet the demands of various lighting tasks. These lighting devices can be broadly defined by two categories: fixed and portable. While all lighting devices can be made portable, portable lighting in this context refers to those that are made to be repositioned by hand by a user to illuminate various tasks, while fixed lighting devices, on the other hand, are made to be installed in a single location where the fixture remains. Many portable lights include a mounting device, such as a magnet or a clip, for temporarily holding the light in a position. Examples of portable lighting devices include flashlights and work lights such as those used by auto mechanics to illuminate specific parts of an auto while work is being performed. Examples of fixed lighting devices include down lights in the ceiling of a home or street lights which are mounted on a light pole to illuminate a street at night.
Portable lights can be powered using either AC or DC power sources to cause the lamp of the lighting device to produce light. Typically a portable light with an AC power source relies on an electrical cord with a power plug for connecting the light to a wall socket to receive AC power. Lights with DC power sources typically have one or more batteries to provide the power to generate light. Depending on the type of lamp used in the lighting device, other electronics, such as a driver circuit, may also be required to convert the AC or DC power to a form that is usable by the particular type of lamp used.
Light emitting diodes (LEDs) are one type of lamp that are used in portable lights which require the use of a driver circuit to convert AC power to a relatively low voltage DC power. Typical wall sockets in the United States are 120V AC while typical LEDs require less than 10V DC. However, even though LED lamps often require the use of a driver circuit, these lamps are becoming increasingly popular as a light source because of their high efficiency and long life.
LEDs are semiconductor devices which have a semiconductor die that produces the light in response to receiving power in the correct range of voltage and current. LEDs are often provided with a lens attached or close to the semiconductor die to direct light from the die so that the light can be more fully utilized. Secondary optics in the lighting device can also be used to reform the beam of light from the LED to attempt to meet the needs of the intended user.
Conventional portable lighting devices are equipped with either fixed focus optics or with adjustable focus optics. Light distribution in fixed focus lighting devices is usually determined by the source of light in combination with one or more optical elements such as a reflector or lens. In these devices, the light distribution is not adjustable. This means that light is spread over or focused on a fixed area relative to the lighting device and the user must move the lighting device in order to change the area that is illuminated. This can be a problem in situations where the lighting device is temporarily attached to hold the device fixed at an available position but the light from the device is not illuminating the desired task correctly. Conventional flashlights have a non movable reflector that is positioned under a protective transparent material. In these flashlights, the focus of the light is fixed relative to the light source. In these and in similar fixed focus devices, the optics are not replaceable because of space, cost and other considerations.
Another fixed type optic involves the use of diffusion screens to spread the illumination. Conventional diffusion screens have textured surfaces which generally provide poor control and waste light because they randomly disperse light. Moreover, these diffusion screens do not provide for adjustability in the light dispersion.
Conventional adjustable focus optics can cause non-uniformities when the distance between the optic and the light source is changed. One example of this involves flashlights that use a parabolic reflector that is moved toward and away from the light source to adjust the light distribution. In this instance, moving the reflector towards or away from the light source results in an out of focus condition where a dark central region, sometimes referred to as a “donut hole”, is created. Of course having a dark central region in the light distribution is counter productive since it diminishes the ability to see what is in the center of the illuminated task.
The present invention provides a highly advantageous lighting device and method that are submitted to resolve the foregoing problems and concerns while providing still further advantages, as described hereinafter.